This invention relates to relatively large-scale irrigation systems used to water turf and other planted areas along freeways, and at golf courses, cemetaries, parks, and the like. These areas are preferably watered at night for more effective irrigation, and to avoid interference with normal daytime usage.
Automatic control systems are commercially available for unattended actuation of such irrigation systems on a preselected and adjustable time cycle appropriate to weather conditions and the particular grass or landscaping material being watered. These control systems are helpful in reducing labor expense, and in providing the proper amount of water to each irrigated area during night hours.
Two problems are recognized in irrigation systems of the type just described. The first problem involves line drainage through the lower sprinkler heads when the main control valve is shut off and the heads are installed on sloping terrain. In a typical irrigation system, a substantial amount of water is in the lines downstream of the control valve. This water dribbles out of the lower sprinkler heads by gravity flow, causing flooding of the turf or planted areas adjacent these heads. This flooding may retard or destroy plant growth, and can result in the area around the heads becoming muddy and temporarily unusable. Drainage of the lines can further result in destructive water-hammer conditions if the main supply is subsequently opened to permit high-velocity flow into the empty downstream lines. Soil and clogging debris may also be drawn into higher-level heads as a result of reduced pressure in the lines during drainage flow.
A second and more serious problem arises when a sprinkler head is damaged or removed by vandals, resulting in uncontrolled flow and severe flooding of the adjacent area upon automatic actuation of a watering cycle. Water flow rate through an open-ended pipe is much higher than when the pipe is terminated in a sprinkler head due to the flow impedance of and significant pressure drop across the head. The irrigation system is designed on the basis of known line lengths and sprinkler-head characteristics to deliver a particular amount of water to the sprinkled area for a known water-main pressure and operating time. This controlled water distribution is destroyed when one or more heads are damaged or removed, with serious water loss and flooding being the result.
This problem is particularly acute in irrigation systems for watering sloping planted areas along the sides of freeways and major highways. It is not uncommon for an out-of-control vehicle to leave the road and tear one or more sprinkler heads from the supporting water lines. The sprinkler heads are relatively expensive, and have also frequently been stolen by vandals.
Either damage or removal of a head results in an open-ended line pouring out large amounts of water which floods over the roadway if the failure is not promptly detected and the control valve closed. The potential for vehicle accidents on a suddenly flooded section of roadway is so high that many municipalities require constant surveillance by a workman whenever the irrigation system is operated. This supervision involves additional labor expense at premium rates which usually must be paid for work performed through the night.
The dual-function valve of this invention solves these problems by preventing dribbling flow through the lowermost sprinkler after shutoff of the main control valve, and by sensing and terminating excessive flow caused by a damaged or missing sprinkler head. Drainage-preventing check valves are known for performing the first of these functions, and check valves have previously been used in pneumatic equipment to prevent whipping flexible lines in high-pressure air systems. The new valve described below, however, solves both problems in a simple and economical assembly which is well adapted for use in large-scale irrigation systems.